The present invention relates to a 3-position stopping cylinder having an intermediate stopping position between an advance stroke end and a retreat stroke end.
A 3-position stopping cylinder of this kind has been used for rotationally driving a latch key in a load port used in a manufacturing process of semiconductor wafers, for example, as disclosed in JP 2001-2428610A publication.
The 3-position stopping cylinder is constituted as shown in FIG. 14. That is, the cylinder comprises a piston 2 and a piston rod 3 which can freely advance and retreat in the interior of the cylinder tube 1, a spring receiving member 4 which is movably attached on the piston rod 3, a stopper 5 and a cylinder cover 6 which restricts movement of the spring receiving member 4 in one direction, a first spring 7 which is provided between the spring receiving member 4 and the piston 2, a recessed portion 3a which is formed at one end of the piston rod 3, and a stop pin 9 which is biased by a second spring 8 in a direction in which it is engaged with the recessed portion 3a. 
When the first port 11 is set in a high pressure and the second port 12 is set in a low pressure, the piston 2 moves to the retreat stroke end and the spring receiving member 4 abuts on the cylinder cover 6 so that the first spring 7 is compressed. In this state, when the first port 11 is changed to a low pressure, the piston rod 3 is advanced by the first spring 7 so that the stop pin 9 stops at an intermediate position where it is engaged with the recessed portion 3a. In this state, further, when the second port 12 is changed to a high pressure, the stop pin 9 retreats due to fluid pressure to be disengaged from the recessed portion 3a, so that the piston rod 3 moves to the advance stroke end.
In such a conventional 3-position stopping cylinder, since the stop pin 9 which has been biased by the second spring 8 is provided at the cylinder tube 1 side and the recessed portion 3a is provided at the piston rod 3 side in order to stop the piston rod 3 at the intermediate position, it is inevitable that the structure of the cylinder is complicated and the cylinder is large-sized in an axial direction and in a diametrical direction thereof.
Also, when the piston rod 3 is advanced from the intermediate stopping position, both the ports 11, 12 must once be pressurized for disengaging the stop pin 9 securely, and therefore it is necessary to conduct pressurization and exhaust of both the ports. For this reason, such a problem cannot be accommodated by one 3-position valve and it is necessary to provide two 2-position 3-port valves.
A technical object of the present invention is to provide a 3-position stopping cylinder where a piston rod can be stopped at an intermediate position with a simple mechanism without providing the stop pin or the recessed portion required conventionally.
Another technical object of the present invention is to provide a 3-position stopping cylinder apparatus where the 3-position stopping cylinder is constituted so as to be able to stop at three positions using a single switching valve.
In order to solve the above-described problem, according to the present invention, there is provided a 3-position stopping cylinder, comprising: a hollow cylinder main body which has a head side end wall and a rod side end wall at its both ends; a main piston which is disposed in the interior of the cylinder main body slidably in an axial direction thereof and where a rod side pressure receiving face to which a piston rod is attached and a head side pressure receiving face opposed thereto are different in pressure receiving area from each other; a head side pressure chamber and a rod side pressure chamber which are formed on both sides of the main piston; a pusher which is disposed in the interior of the cylinder main body at a position closer to the head side end wall or the rod side end wall rather than the main piston so as to be movable in the axial direction independently from the main piston and which has a stroke shorter than that of the main piston and serves as both means for pushing the main piston from an stroke end back to an intermediate stopping position and means for stopping the main piston at the intermediate stopping position; and pressing means for causing the pusher to displace up to the intermediate stopping position.
In the 3-position stopping cylinder having the above-described constitution, the piston advances and retreats by alternately supplying pressure fluid to both the pressure chambers on the head side and the rod side. Then, when pressure fluids with the same pressure are simultaneously supplied to both the pressure chambers in a state that the piston stops at a stroke end on the side where the pusher has been provided, the piston moves towards the intermediate stopping position because the composite force of a fluid pressure acting force and an acting force due to the pusher is larger than a fluid pressure acting force acting on the pressure receiving face on the opposite side. When the piston moves up to this intermediate stopping position, the pusher stops at that position, so that the acting force from the pusher does not act on the piston and only fluid pressure acting forces acting on the pressure receiving faces on both the sides acts on the piston. For this reason, the piston is put in a state that it has been pressed on the pusher due to a difference between the fluid pressure acting forces based on an area difference between the pressure receiving faces on the both sides, and it stops at the intermediate stopping position.
Thus, according to the present invention, the cylinder can be stopped at the three positions with a simple mechanism utilizing the pressure receiving area difference between the both faces of the piston and the pusher, and it is unnecessary to provide a stop pin or a recessed portion which is required conventionally.
In the present invention, the pressure receiving areas of both the faces of the main piston are constituted such that the pressure receiving area on a pusher-providing side is kept small and the pressure receiving area on the opposite side thereto is kept large while the main piston is positioned in a stroke range of at least the stroke end on the pusher-providing side to the intermediate stopping position of the whole stroke.
Also, according to one specific constitution aspect of the present invention, the pusher is formed in a hollow sleeve shape and the pressing means is a spring; and the pusher is disposed in the interior of the cylinder main body at a position closer to the rod side end wall rather than the main piston in a state that the pusher has been supported through an outer periphery thereof to an annular guide portion provided to the cylinder main body, the piston rod penetrates the interior of the pusher, a distal end portion of the pusher projects into the rod side pressure chamber and a rear end portion thereof abuts on the spring, and the pusher has a stopper engaged with the guide portion at a position of an advanced end thereof.
According to anther specific constitution aspect of the present invention, the pusher is formed in a short shaft shape and the pressing means is a spring; the pusher is disposed in a receiving chamber positioned at a position closer to the head side end wall rather than the main piston in the interior of the cylinder main body and is biased towards the main piston by the spring; the main piston has a shaft portion extending from an end face thereof on the head side into the receiving chamber in a sealed state to abut on the pusher, and the shaft portion has a diameter larger than that of the piston rod.
According to still another specific constitution aspect of the present invention, the pusher is provided with an annular auxiliary piston portion and a hollow auxiliary rod portion extending from the auxiliary piston portion, and the pressing means is pressure fluid; the cylinder main body has a auxiliary piston chamber formed at a position adjacent to the rod side pressure chamber via an annular partition wall, the auxiliary piston portion of the pusher is slidably received in the auxiliary piston chamber, the auxiliary rod portion is slidably supported to the partition wall via an outer periphery thereof to extend into the rod side pressure chamber, the piston rod penetrates these auxiliary piston portion and the interior of the auxiliary rod portion, and an auxiliary pressure chamber for supplying the pressure fluid is formed on one side of the auxiliary piston portion.
The rod side pressure chamber and the auxiliary pressure chamber mutually communicate with each other via a passage provided inside or outside the cylinder main body.
According to still another specific constitution aspect of the present invention, the pusher is formed in a piston shape, the pressing means is a pressure fluid, the pusher is disposed in the interior of the cylinder main body so as to be slidable in a sealed state in a auxiliary piston chamber provided at a position closer to the head side end wall rather than the main piston, an auxiliary pressure chamber for supplying the pressure fluid is formed on one side of the pusher, the main piston has a shaft portion extending from an end face of the head side towards the pusher in a sealed state, and the shaft portion has a diameter larger than that of the piston rod.
According to still another specific embodiment of the present invention, the cylinder main body has an auxiliary piston chamber formed at adjacent to the head side pressure chamber and a sliding hole connecting the head side pressure chamber and the auxiliary piston chamber, the pusher is formed in a piston shape and is disposed in the auxiliary piston chamber so as to be slidable in a sealed state, a rod portion which extends towards the main piston and which is fitted into the sliding hole in a sealed state at an advance stroke end of the pusher is provided one side of the pusher, an auxiliary pressure chamber in which pressure fluid which is the pressing means is formed on the other side of the pusher, the main piston has an shaft portion opposed to the rod portion on its end face on the head side, and the shaft portion has a diameter larger than that of the piston rod and has a length where the shaft portion can be fitted in the sliding hole in a sealed state only when the main piston is positioned in a stroke range from the retreat stroke end to the intermediate stopping position.
Also, according to the present invention, a 3-position stopping cylinder apparatus is constituted by connecting the above-described 3-position stopping cylinder to a common pressure fluid source via a switching valve of a single 3-position pressure center type.